linux-kernel - Re: [External Mail] [RFC PATCH] mm/mempolicy: Weighted interleave auto-tuning

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Message-ID: <Z1xglcL7wb_2IwnS@PC2K9PVX.TheFacebook.com>
Date: Fri, 13 Dec 2024 11:28:05 -0500
From: Gregory Price <gourry@...rry.net>
To: Hyeonggon Yoo <hyeonggon.yoo@...com>
Cc: Joshua Hahn <joshua.hahnjy@...il.com>, kernel_team@...ynix.com,
	"rafael@...nel.org" <rafael@...nel.org>,
	"lenb@...nel.org" <lenb@...nel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	김홍규(KIM HONGGYU) System SW <honggyu.kim@...com>,
	"ying.huang@...ux.alibaba.com" <ying.huang@...ux.alibaba.com>,
	김락기(KIM RAKIE) System SW <rakie.kim@...com>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"Jonathan.Cameron@...wei.com" <Jonathan.Cameron@...wei.com>,
	"dave.jiang@...el.com" <dave.jiang@...el.com>,
	"horen.chuang@...ux.dev" <horen.chuang@...ux.dev>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"kernel-team@...a.com" <kernel-team@...a.com>
Subject: Re: [External Mail] [RFC PATCH] mm/mempolicy: Weighted interleave
 auto-tuning

On Fri, Dec 13, 2024 at 03:19:20PM +0900, Hyeonggon Yoo wrote:
> On 2024-12-11 06:54 AM, Joshua Hahn wrote:
> > This patch introduces an auto-configuration for the interleave weights
> > that aims to balance the two goals of setting node weights to be
> > proportional to their bandwidths and keeping the weight values low.
> > This balance is controlled by a value max_node_weight, which defines the
> > maximum weight a single node can take.
> 
> Hi Joshua,
> 
> I am wondering how this is going to work for host memory + CXL memory
> interleaving. I guess by "the ACPI table" you mean the ACPI HMAT or CXL
> CDAT, both of which does not provide the bandwidth of host memory.

Then your BIOS vendor needs to fix their ACPI table generation, because
HMAT can absolutely contain that information.

[078h 0120   2]               Structure Type : 0001 [System Locality Latency and Bandwidth Information]
[07Ah 0122   2]                     Reserved : 0000
[07Ch 0124   4]                       Length : 00000030
[080h 0128   1]        Flags (decoded below) : 00
                            Memory Hierarchy : 0
                   Use Minimum Transfer Size : 0
                    Non-sequential Transfers : 0
[081h 0129   1]                    Data Type : 00
[082h 0130   1]        Minimum Transfer Size : 00
[083h 0131   1]                    Reserved1 : 00
[084h 0132   4] Initiator Proximity Domains # : 00000001
[088h 0136   4]   Target Proximity Domains # : 00000002
[08Ch 0140   4]                    Reserved2 : 00000000
[090h 0144   8]              Entry Base Unit : 00000000000003E8
[098h 0152   4] Initiator Proximity Domain List : 00000000
[09Ch 0156   4] Target Proximity Domain List : 00000000
[0A0h 0160   4] Target Proximity Domain List : 00000001
[0A4h 0164   2]                        Entry : 006E
[0A6h 0166   2]                        Entry : 01FE

[0A8h 0168   2]               Structure Type : 0001 [System Locality Latency and Bandwidth Information]
[0AAh 0170   2]                     Reserved : 0000
[0ACh 0172   4]                       Length : 00000030
[0B0h 0176   1]        Flags (decoded below) : 00
                            Memory Hierarchy : 0
                   Use Minimum Transfer Size : 0
                    Non-sequential Transfers : 0
[0B1h 0177   1]                    Data Type : 03
[0B2h 0178   1]        Minimum Transfer Size : 00
[0B3h 0179   1]                    Reserved1 : 00
[0B4h 0180   4] Initiator Proximity Domains # : 00000001
[0B8h 0184   4]   Target Proximity Domains # : 00000002
[0BCh 0188   4]                    Reserved2 : 00000000
[0C0h 0192   8]              Entry Base Unit : 0000000000000064
[0C8h 0200   4] Initiator Proximity Domain List : 00000000
[0CCh 0204   4] Target Proximity Domain List : 00000000
[0D0h 0208   4] Target Proximity Domain List : 00000001
[0D4h 0212   2]                        Entry : 1200
[0D6h 0214   2]                        Entry : 0064

Obviously if information is missing, then manual is the only way forward.

> > +		The maximum interleave weight for a memory node. When it is
> > +		updated, any previous changes to interleave weights (i.e. via
> > +		the nodeN sysfs interfaces) are ignored, and new weights are
> > +		calculated using ACPI-reported bandwidths and scaled.
> > +
> 
> At first this paragraph sounded like "previously stored weights are
> discarded after setting max_node_weight", but I think you mean
> "User can override the default values, but defaults values are calculated
> regardless of the values set by the user". Right?
> 

Agree that these comments need clarification, we'll workshop it.

~Gregory